Pneumatic hammer.



E. H. LAGERSTRUM. PNEUMATIC HAMMER. APPLICATION FILED JUNEZ, 1911.

1,017,562. e Patented Feb. 13, 1912.

ERNST HJALMAR LAGERSTIRbM, OF STOCKHOLM, SWEDEN.

PNEUMATIC HAMMER.

Specification of Letters Patent.

Patented Feb. 13, 1912.

Application filed June 2, 1911. Serial No. 630,792.

.drilling machine, hammer or the like without distributing valve or anyother distributing member. In such machines the piston generally iscarried out as a differential piston and the air pressure used forreturning the piston acts in one type of machines on the shoulderbetween the two piston portions and in another type on the fore or outerend surface of the piston portion of the smaller diameter. In the firstmentioned type it is necessary in order to reach a reliable function ofthe machine that the-piston portion of the larger diameter be polishedvery accurately to fit in an airtight manner in the corresponding partof the cylinder. If the said piston port-ion has not been polishedaccurately enough or if it becomes worn and does not move in an airtightmanner in the cylinder, the air acting on the shoulder between the twopiston portions leaks pastthe piston portion of the larger diameter intothe space behind this piston portion, where it counteracts the returningof the piston and thus reduces the efficiency of the machine. Theleakage can be obviated only by inserting a new piston which on accountof the difliculty of polishing the pistons cannot be made at the placewhere the machine is used. The second type referred to above has beenconstructed with the view to obviate the disadvantage just described. Inthis type the air pressure, as mentioned, acts on the fore end of thepiston portion of the smaller diameter, while the cylinder space infront of the shoulder between the two cylinder portions is in opencommunication with the atmosphere. The air pressure that eventuallyleaks into said space in the one direction or the other will thus bewithout influence on the function of the machine inasmuch as it escapesdirectly into the atmosphere. It is however necessary to prevent the airpressure acting on the fore end of the piston from leaking past the toolinserted in the cylinder. For this purpose it has been proposed toprovide between the piston and the tool an intermediate piece fitting inan airtight manner in the cylinder and freely movable in the latter.This device however, is objectionable in that the efliciency of themachine is greatly reduced on account of the so called dead strokeswhich occur very often and are due to the fact that said intermediatepiece cannot always follow the movements of the tool.

The object of the present invent-ion is to overcome the saiddisadvantages, and the present invention consists, briefly, in that thepiston in addition to the usual forward portion of reduced diameter hasat the forward end of said reduced forward portion an extension of stillsmaller diameter which fits in an airtight manner in the forward end ofthe cylinder and acts directly on the tool inserted in the usual mannerin the cylinder. The air pressure used for returning the piston from thetool acts on the shoulder between the said extension and theintermediate piston portion, while the cylinder space in front of therear and largest portion of the piston is in open communication with theatmosphere in the ordinary well known manner,

In the accompanying drawing I have shown one embodiment of my inventionapplied to a rock drilling machine.

Figure 1 shows a longitudinal section of the machine on line AA in Fig.2, while Fig. 2 shows a cross-section on line BB in Fig. 1, the pistonbeing removed.

As is shown in the drawing, the piston comprises a rear large portion 1and a portion 2 of reduced diameter in front of the portion 1, and thesaid portion 2 is provided at its forward end with an extension 3 ofstill smaller diameter, which extension 3 fits in an airtight manner inthe corresponding part of the cylinder 4:. The air pressure is admittedin the usual manner through a cock 5 and flows through the channel 6 toa point in front of the forward end of the piston portion 2, and returnsthe piston from the bit 7. When the forward end of the piston portion 2passes, incidental to the backward movement of the piston, the port orports 8, the air pressure passes through said port or port-s and thechannel or channels 9 into the cylinder space behind the large portion 1of the piston, and forces the piston toward the hit. As soon as thepiston portion 2 has, incidental to the forward movement of the piston,covered the port or ports 8, the air pressure behind the piston acts onthe latter by expansion until the piston portion 1 uncovers the usualexhaust ports 10, whereupon the piston is again forced backward, and soon. The air pressure that eventually leaks past the piston portions 1and 2 into the cylinder space in front of the shoulder between saidpiston portions escapes through exhaust ports 11 connecting in wellknown manner said cylinder space directly with the atmosphere, while theair pressure that eventually leaks past the forward extension 3 escapesthrough a port or ports 12.

Having now described my invention, what I claim as new, and desire tosecure by Letters-Patent, is:

In a pneumatic rock-drilling machine or the like in which nodistributing valve or any other special distributing member is employed,the combination of a cylinder and a piston; the piston being ofdifferential type and having a large rear portion and an intermediateportion of smaller diameter than the rear port-ion arranged in front ofsaid rear portion and also having at the forward end of the intermediateport-ion an extension of smaller diameter than said lntermediateportion, and the cylinder having a forward interior portion whichreceives in an airtight manner the said extension of the piston, and thepiston and the cylinder being so constructed and relatively arrangedthat the air pressure for returning the piston from the tool or bit actson the shoulder between the said extension and the intermedi ate portionof the piston, and the cylinder being further provided with a space infront of the shoulder between the intermediate portion and the rearportion of the piston, which space communicates directly with theatmosphere.

In testimony that I claim the foregoing as my invention, I have signedmy name in presence of two subscribing witnesses.

ERNST HJALMAR tieresrntn.

IVitnesses:

CARL DELMAR, JOHN DELMAR.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. G.

